Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first image of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a second image thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIG. 1 through FIG. 2 . The process or period in which one image transitions to another forms no part of the claimed design.

The dash-dot broken line illustrating boundaries of the display screen or portion thereof. The remaining broken lines, including all text, illustrate portions of the display screen or portion of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 